Blood samples were also taken to measure the levels of circulating nitric oxide, which indicates harmful oxidation associated with traffic fumes.

By BMJ Specialty Journals,To gauge the levels of exposure to traffic fumes, the research team assessed the amount of a chemical called 1-OHPG in the urine of 47 female motorway toll-booth operators and 27 female office workers.

The 20 toll booths were located on a motorway 10 km south of Taipei, Taiwan, and have the highest traffic density of any toll station in the country.

To test the effects of exposure, they measured 8-OHdG in the urine. This is an indicator of DNA damage caused by oxygen free radical activity in the body.

Blood samples were also taken to measure the levels of circulating nitric oxide, which indicates harmful oxidation associated with traffic fumes.

The operators worked in eight hour shifts, for four consecutive days, before taking a day off. During their shift, they took breaks of between 30 and 45 minutes every couple of hours. They regularly changed lane booth, working a rotation system.

Smoking also increases the amount of urinary 8-OHdG, and there were more smokers among the office workers.

But levels of urinary 8-OHdG were an average of 90% higher among the non-smoking toll booth operators than they were among the office workers. Levels of nitric oxide were an average of 30% higher.

The levels of 1-OHPG were strongly linked to the levels of 8-OHdG. The higher the 1-OHPG, the higher was the 8-OHdG. And this held true even after adjusting for smoking or mode of transport to work.

The authors conclude that traffic fumes boost oxygen free radical activity and therefore DNA damage, and that environmental levels should be curbed to protect people's health.